He wrote The Man Called Deng Majok: A Biography of Power, Polygyny, and Change (Yale University Press, 1986) about his father, the renowned Paramount Chief of the Ngok Dinka in the Sudan, which Francis was kind enough to autograph for me.

Polygyny had some social utility, because it increased the number of children, and this gave added prestige and power to the family, as slavery had utility because it provided a labor force; but both were weaknesses in ancient society, because they did not tend in the long run to human welfare.